Electronic wiring substrate

ABSTRACT

An improved electronic wiring board having a thermistor and at least one blood gas sensor supported, in close relation, one to the other, on one side of the board and a heater supported on the other side of the board to provide heat in response to temperature sensed by the thermistor, to at least the region where the thermistor and the blood gas sensor are positioned on the board to control the temperature of the region of the board within a narrow distribution of temperatures.

This application is a continuation-in-part application of Ser. No.07/721,030 filed Jun. 26, 1991, now abandoned.

FIELD OF THE INVENTION

The present invention is related to an improved electronic wiringsubstrate like a wiring board useful for detecting one or more analytesand their amounts in fluid samples.

BACKGROUND OF THE INVENTION

Numerous methods and apparatus exist in the art for measuring chemicalcomponents of fluids, and current technology utilizes many types ofsensors for detecting components, analytes, in numerous types of fluids.For example, some of these range from oxygen sensors for detectingoxygen in air for control of the air and fuel ratio for combustion ininternal combustion engines to multiple phase sequential analyzers forqualitative and/or quantitative measurement of constituents or analytesof blood. For instance, the measurement of blood gases, usually ameasure of the partial pressures of oxygen and carbon dioxide, alongwith the pH from a sample of arterial blood gives the state of the acidbase balance or the effectiveness of both the respiratory andcardiovascular systems of the human or vertebrate body. These varioustypes of sensors can be prepared by various techniques including layeredcircuit or integrated circuit technologies, as for example, thick film,thin film, plating, pressurized laminating and photolithographicetching, and other like silk screening processes.

In many of the existing measurement methods, when the fluid is a liquidor liquid with a dissolved gas with or without the presence of solids,it may be necessary to transport a sample to a central location fortesting. With centralized testing, the bulky, stationary, elaborate andsophisticated equipment performs the analysis on a practically endlessnumber of samples. An example of this is the qualitative and/orquantitative measurement of constituents or analytes of blood. Forinstance, the measurement of blood gases, usually a measure of thepartial pressures of oxygen and carbon dioxide, along with the pH from asample of arterial blood gives the state of the acid base balance or theeffectiveness of both the respiratory and cardiovascular systems of thehuman or vertebrate body. For measuring constituents of blood, the bloodsample is drawn from the patient and usually, as in the case of bloodgases, transported to a central location for testing.

This technique of transporting the sample to stationary measuringequipment can lead to problems. Ingenious technology has broachedsolutions to maintain the original composition of the fluid duringtransportation. Elaborate designs for syringes used in taking the bloodsamples overcame some problems that resulted in inaccurate readings ofthe particular chemical constituent being measured. For instance, indetermining blood gas composition, the problem of air contamination inthe collected sample was solved by the use of liquid heparin as ananticoagulant. Unfortunately, this introduced a sample dilution problem.Subsequent development resulted in the use of heparin in the dry stateas opposed to the liquid state to avoid this dilution. Also, elaboratedesigns provided for proper mixing of the sample after transportationbut before testing. Even with these improvements, there are many reportsin the literature that suggest that the values obtained in themeasurement of blood gases depend on the type of measuring equipment andthe technique for sample collection.

The art also has attempted to develop more portable measuring equipmentrather than the fairly expensive nonportable equipment that engender theelaborate and cumbersome transportation techniques. Devices that arevery portable could shorten or overcome transporting the samplealtogether so that a patient's blood gases could be measured at thebedside in a manner similar to measuring a patient's temperature. U.S.Pat. Nos. 3,000,805 and 3,497,442 show two such devices. The former haselectrodes located on a syringe plunger and the latter has electrodesplaced on the syringe well to conduct the measurements. The electrodesare the sensing devices for the blood gases. In the allowed U.S. patentapplication Ser. No. 07/343,234, now U.S. Pat. No. 5,046,496. Applicantsassignee describes and claims a portable blood gas sensor which includeselectrodes fabricated from a conventional silk screening process wherethe electrodes are screened on to a ceramic substance. Typically theseelectrodes are used along with an electrolyte and analyte permeablemembrane that covers the sensor. Some of these membranes may behydratable membranes that can be stored in a dry state and hydrated justprior to use.

The utilization of portable equipment to obtain accurate analysisreports while using a disposable device could be advanced withimprovements in electronic circuit board design.

Accurate sensing of the ambient temperature of the wiring board isrequired to precisely control the heater to ultimately maintain, withina narrow distribution of temperatures, the desired operating surfacetemperature on the wiring board in the region the several sensors. Alsothe accurate sensing of temperature is important is the area ofmeasuring two phase calibrant liquids so that the calibrant values canbe corrected for the most recent storage temperature.

Placement of the all of the components, including the heater, on thewiring board is also very important to obtain the maximum utility andcapability of these components and minimize power consumption.

SUMMARY OF THE INVENTION

The improved electronic wiring board of the present invention has anonconducting substrate, a thermistor and at least one analyte sensorsupported, in close relation, on the substrate, and a heater, alsosupported on the substrate, to provide heat in response to temperaturesensed by the thermistor to at least the region where the thermistor andthe blood gas sensor are positioned on the board to thereby control thetemperature of the region of the board within a narrow distribution oftemperatures and thereby increase the sensor's accuracy, and connectingmeans supported on the board for connecting the board to an externalelectrical source.

In a narrower aspect of the present invention the improved electronicwiring substrate is manufactured using thick film or thin film layeredcircuit technique or a combination of these, and the thermistor and theone or more analyte sensors are supported in the same plane on thesubstrate wherein the analyte sensors are blood gas sensors of one ormore of the following types: an oxygen sensor, a carbon dioxide sensor,and a pH sensor. Also the connecting means includes plurality ofexternal leads, and a resistor is supported on the substrate on the sameside as the heater and commonly connected to one of the external leadswith the thermistor, dividing the voltage therebetween. Although it ispossible to have the resistor and the heater each electrically connectedto external leads, the temperature coefficient of the thermistor can bepositive or negative and the temperature coefficient of the resistor issubstantially zero. Also the thermistor and resistor values are allowedto vary over several orders of magnitude as long as the two can be madeequal at the calibration temperature. Additionally, the connecting meansfurther includes a plurality of electronic conducting pathwaysindividually and electrically connecting each of the sensors and thethermistor with external leads provided on the substrate at the end ofthe pathways. Also the heater is powered by a controlled DC voltagewhereby the heater is regulated by a combination of proportional,integral and/or derivative controls thereby reducing the amount ofovershooting or undershooting by the heater of a predeterminedtemperature. The external leads are positioned on the same side of thesubstrate as the resistor and the heater.

Another aspect of this invention is to provide an improved electronicwiring substrate wherein the electronic conducting pathways individuallyand electrically connecting each of the sensors and the thermistor onone side of the board with external leads provided on the other side ofthe board through a plurality of holes in the board.

Another aspect of this invention is to provide an improved electronicwiring substrate wherein the temperature sensor including the thermistorand the resistor is calibrated by laser trimming of the resistor toproduce a ratiometric output proportional or inversely proportional totemperature.

A further aspect of this invention is to provide an improved electronicwiring substrate wherein the oxygen sensor is an electrochemical celland includes a anode and a cathode, each connected to an external lead.Also the oxygen sensor includes an oxygen permeable membrane covering,in a fluid tight manner, and an opening in the board contains anelectrolyte, and the anode is grounded on the board to thereby assurethat the potential of the electrolyte is the same as the anodepotential.

Another aspect of this invention is to provide an improved electronicwiring substrate wherein there is at least one reference electrode, toprovide an accurate reference potential, supported on the board and iselectrically connected to a electronic conducting pathway. Although itis possible to have one reference electrode present on the substrate andit is supported on the substrate and it is electrically connected to aelectronic conducting pathway extending from the anode. Thenonconducting substrate is a flat substantially thin ceramic substratelayer that has a patterned metallic layer provided on the ceramicsubstrate layer. The metallic layer can be formed on the substrate bydepositing a metallic printing paste on the substrate to form electronicconducting pathways and the electrodes of the sensors and the electrodeof a reference electrode. The metallic layer can be encapsulated with atleast one layer of a chemically stable and moisture resistantencapsulant that provides electrical isolation of the electronicconducting pathways from the electrolyte to sample like blood. Thewiring substrate as described can operate even after several months ofstorage. The thermistor provided on the ceramic substrate layer, can beencapsulated with at least one substantially thin layer of a chemicallystable and moisture resistant encapsulant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top planar view of one side of the wiring substrate of thepresent invention, having electrodes and a thermistor.

FIG. 2 is a planar view of the other side of the wiring substrate ofFIG. 1 having a resistor and a heater that traverses the board and anumber of leads through the substrate from the side depicted in FIG. 1to provide an external electrical connection from the substrate.

FIG. 3 is a planar view of the one side of the wiring substrate of thepresent invention, having an arrangement of three analyte sensors withtwo reference electrodes and a thermistor with accompanying patternedand layered circuitry.

FIG. 4 is a planar view of the one side of the wiring substrate of abroad aspect of the present invention having one sensor and a thermistoraxially aligned and one reference electrode spaced apart from that axisand having accompanying patterned and layered circuitry.

FIG. 5 is a block diagram of the monitoring means and its connectionwith the electronic wiring substrate.

FIG. 6 is a block diagram of the flow chart of the software for theanalyzer.

DETAILED DESCRIPTION OF THE INVENTION

Similar numerals are used throughout all of the drawings to denotesimilar features.

FIG. 1 is a top planar view of one side of the wiring substrate,hereinafter referred to as "board" with at least one electrochemicalsensor 10 of the present invention, where the components have particularshapes. Any other shapes than those shown in FIG. 1, that are known tothose skilled in the art for the particular components, can be used.

The improved wiring board 10 may be produced from any number of wellknown layered circuit technologies, as for example, thick film, thinfilm, plating, pressurized laminating and photolithographic etching,however, the thick film technique is preferred.

The substrate 12 on both sides of the board 10 is any glass or ceramicincluding sheet or chip or nonconducting substrate like wood ornonconducting polymers or commercially available frit that can be usedas the substantially smooth flat surface of the substrate layer 12.Nonexclusive examples include borosilicate glass as is known to thoseskilled in the art for producing thick film or layered circuits. Anonexclusive but preferred example of which includes a ceramic basehaving around 96% Al203 such as that available commercially from CoorsCeramic Company, Grand Junction, Colo.

The substrate layer 12 is essentially flat and any substrate known tothose skilled in the art for forming printed wiring circuits can beused. It is preferred that the composition of the substrate can endurethe presence of electrolyte that has a pH in or over the range of 6 to 9and remain unaffected for a substantial period of time.

As can best be seen in FIG. 1, the board 10 is provided with a number ofelectrodes and more particularly, electrodes useful in the measurementof blood gas oxygen, carbon dioxide and pH. The board 10 is alsoprovided with a thermistor and resistor arrangement to indicate thetemperature at any time on the board 10 as well as reference electrodesfor establishing an accurate reference potential; all of which will bedescribed in further detail below.

On the substrate layer 12 is a patterned metallic layer 14 with a numberof extensions which act as the electronic conducting pathway between avoltage or current source external to the board 10 (not shown) and eachof the components. The extensions constitute the transmission section,where each extension has a component at its end. The several extensionsalso have the ability to transmit changes in voltage from the componentsof the board 10 to an electronic analyzing module as shown in FIGS. 5and 6.

The pH sensing electrode 16 is located at the end of extension 18; thecarbon dioxide sensing electrode 20 is located at the end of extension22; the oxygen sensor 24 is provided with an anode 26 located at the endof extension 28; the reference electrode 30 is located at the end ofextension 32 which extends from anode 26 of the oxygen sensor 24; theoxygen sensor 24 is further provided with a cathode 34 which is locatedat the end of extension 36; thermistor 38 is located at the end ofextensions 40 and 42.

As shown in FIG. 2, the patterned metallic layer 14 has metallicexternal leads 46-60 on the other side of the substrate 12. Although theexternal leads are shown on the opposite side of the substrate 12, theycan also be on the same surface as their associated metallic leadpatterns and components.

External leads 48-58 are conductively associated with the components onthe FIG. 1 side of the substrate layer 12 and external leads 46 and 60are in metallic electrical conducting contact with a thick film heater74 which is provided on the FIG. 2 side of the substrate layer 12. Theheater 74 traverses the board in a serpentine fashion to provide a gridof heat to the nonelectrically conducting substrate and its functionwill be described below.

External leads 52 and 56 are in metallic electrical conducting contactwith a resistor 76 which is also provided on the FIG. 2 side of thesubstrate layer 12. The resistor is in a half-bridge relationship withthe thermistor 38 and, as such, it commonly shares external lead 52 withthe thermistor 38; thermistor 38 also being in metallic electricalconducting contact with external lead 52. The function of the thermistor38 and resistor 76 arrangement will be described below.

The patterned metallic layer 14 is formed by printing pastes depositedonto a substrate in the desired pattern to act as ohmic conductors.Nonexclusive examples of suitable heat resisting metals include; noblemetals such as platinum (Pt), ruthenium (Ru), palladium (Pd), rhodium(Rh), iridium (Ir), gold (Au) or silver (Ag) or other metalstraditionally used as Clark cells and other ISE's and mixtures thereof.A nonexclusive but preferred example of a suitable paste is a silverpaste of the type produced and available from Electro-ScienceLaboratories, Inc. under the trade designation ESL 9912.

The metallic layer 14 is dried to produce the above noted patternedconductive pathways 18, 22, 28, 32, 36, 38 and 40 of FIG. 1. Any methodknown to those skilled in the art for producing a sufficient thicknessof metallic tracing can be used. Preferably pathway 28 has ground 29.

Preferably, the silver pastes are oven dried and fired at a hightemperature in a furnace. Firing can be accomplished at a temperature inthe range of around 800° C. to 950° C. for a period of around 1 to 20minutes. With this procedure, the thickness of the layer of the metallicconducting tracing is usually in the range of around 0.0005 to 0.001inches. Although the aforementioned are preferred conditions, generalconditions for obtaining a proper thickness can be used where thethickness can be generally range from about 0.0004 to 0.0015 inches.

The aforementioned conductive patterns are encapsulated with a glassceramic mixture or a ceramic insulating material such as alumina orspinal. This encapsulation can range from a total encapsulation toencapsulation except at the end of the metallic pattern.

The aforementioned electrodes are preferably produced by one of thelayered circuit techniques. This involves leaving the respective shapedends uncovered while the metallic patterns are completely covered by theencapsulant. The encapsulation of the metallic patterns can range fromencapsulating each from the other to a sufficient degree for electricalinsulation of the conductive patterns and any conductive layers fromeach other.

As shown in FIG. 1, the encapsulant can extend across the whole boardfrom edge to edge as generally shown at numeral 44. Preferably, thethickness of the encapsulant layer is that which is adequate to seal theunderlining metallic layer and to provide insulation for the metallicpatterns. Preferably, the thickness of the layer is around 20-30microns.

A preferred glass ceramic mixture useful as the encapsulant is the typeproduced and available from Electro-Science Laboratories, Inc. under thetrade designation ESL 4904.

The several electrodes may be masked during the encapsulation to keepthem suitably uncovered for the addition of active materials (e.g.polymer liquids and pre-cut dry film membranes) over the appropriateelectrodes on the surface of the substrate layer 12.

This process involves masking the electrodes by the use of polymer filmcoating on the screen used to screen print the encapsulant. This leavesthe underlying silver exposed to form the electrodes for activematerials. It is also possible to use multiple layers of the metallicconductive layer or encapsulant.

Preferably, the glass composition for the encapsulant as with thesubstrate 12 is selected to possess good chemical stability and/ormoisture resistance and to possess high electrical insulationresistance. Also, the metallic and encapsulant materials are selected sothat they can endure the presence of an electrolyte in a similar manneras the substrate composition.

The geometry of the several electrodes could be made by a laser beam tocarve or cut or trim the electrode, however, they are preferablyprepared by the aforementioned layered circuit technique.

The serpentine formed heater 74 and the resistor 76 on the FIG. 2 sideof the board may be prepared by a number of commercially availabletechniques, however, they are preferably thick film devices prepared bythe aforementioned layered circuit technique.

Holes 62-72 may be drilled by a laser through the substrate 12 toconductively connect the metallic extensions 18, 22, 28, 38, 40 and 36traced on the FIG. 1 side of the substrate layer 12 with theirrespective metallic external leads 48-58 on the FIG. 2 side of thesubstrate layer 12. In general, these openings 62-72 are produced by thefocused laser beam drilling a hole by heating a small volume of materialto a sufficiently high temperature for localized melting and/orvaporization.

The external leads 46-60 may be produced on the other side of the sideof the substrate layer 12 with the same paste and firing as that donefor aforementioned metallic patterns. The metallic external leads 46-60are in metallic electrical conducting contact with the variouscomponents on each side of the board. As before mentioned external leads46 and 60 are in metallic electrical conducting contact with the heater74 and external leads 52 and 56 are in metallic electrical conductingcontact with a resistor 76 which commonly shares external lead 50 withthe thermistor 38; thermistor 38 also being in metallic electricalconducting contact with external lead 50. External lead 58 is inmetallic electrical conducting contact with the CO₂ sensing electrode20; external lead 48 is in metallic electrical conducting contact withthe pH sensing electrode 16; external lead 48 is in metallic electricalconducting contact with the CO₂ sensing electrode 20; external lead 52is in metallic electrical conducting contact with the anode 26 of theoxygen sensor 24, the anode 26 having an electrical ground 27; externallead 52 is also in metallic electrical conducting contact with thereference electrode 30 which is located at the end of extension 32 whichextends from anode 26 of the oxygen sensor 24, the anode 26 and externallead 54 is in metallic electrical conducting contact with the cathode 34of the oxygen sensor 24; external lead 54 is in metallic electricalconducting contact with the cathode 34 of the oxygen sensor 24.

The holes 62-72 have been drilled through the substrate layer 12 andwhen the metallic layers are screened such electrical connections areformed. Alternatively, the metallic external leads 46-60 can be producedand preferably are produced by a very high powered carbon dioxide laser.This can be accomplished by the supplier of the nonconducting substrateand in this case the metallic layer is added to the substrate so eachconducting pathway electrically connects with an external lead.

As described above, the process of masking the electrodes by the use ofpolymer film coating on the screen, is used to screen print theencapsulant. This leaves the underlying silver exposed to form theelectrodes for active materials. It is also possible to use multiplelayers of the metallic conductive layer or encapsulant and the outerlayer of the encapsulant may be solvent or thermoplastically bondableand may include polymers, as for example, acrylates or polyvinylchloride as the major component in the encapsulant. The purpose of theouter coating or encapsulant is to enhance bonding of the activematerials and, in particular, to provide a reliable surface for theattachment of the liquid or solid film type membrane materials.

Each of the sensing electrodes are fabricated to perform their specifictask and may be selected from many commercially available electrodecomponents. The pH electrode 16, CO₂ electrode 24 and the Oxygen sensor24 are each fabricated with a membrane which maintains their respectiveelectrolytes in a fluid tight manner in the cavities or openings inwhich the electrodes are positioned.

The pH electrode 16 and the CO₂ electrode 20 may be similar in regardsto the circuit geometry and electrolyte and may be provided withmembranes suitable for the particular characteristic being measured.

For pH electrode 16, for example, the use of cation permeable andparticularly hydrogen ion permeable membrane may be used. A number ofsuch cationic exchange materials may be utilized, as for example,membranes fabricated from copolymeric vinyl ethers as manufactured by E.I. duPont under registered trademark NAFION.

The membrane for the CO₂ electrode 20 may be fabricated from a widerange of commercially available carbon dioxide permeable polymericmaterials. The electrolytes of the pH electrode 16 and the CO₂ electrode20 are bound by their respective membranes.

The membrane for the oxygen sensor may be fabricated from a polymericmaterial such as polystyrene in an organic or inorganic solvent. Theoxygen permeable electrolyte of the oxygen sensor 24 bathes the anode 26and cathode 34 to provide electrical ionic contact between the two. Theelectrolyte can be any electrolyte known to those skilled in the art forClark Cell as, for example, a saline solution based on potassiumchloride or sodium chloride.

The anode 26 of the oxygen sensor 24 is electrically grounded at 27 toassure that the electrolyte potential does not change and that theopening to the electrolyte is held at some voltage which is the same asthe anode potential so that the electrolyte is grounded in the electrodeconfiguration.

The reference electrode 30, which is located at the end of extension 32and which extends from anode 26 of the oxygen sensor 24, provides ahighly stable reference potential. This reference potential provided bythe reference electrode 30 facilitates accurate measurement of the bloodgases. The reference electrode 30 may be fabricated from a number ofsuitable materials known to those skilled in the reference electrode artsuch as a silver and silver chloride composite using the aforementionedlayered circuit technique.

The thermistor 38 is a thick film thermally sensitive resistor whoseconductivity varies with the changes in temperature. The thermistor 38may be fabricated from a number semi-conductive materials as, forexample, oxides of metals. The thermistor and may be formed and appliedto the substrate layer 12 by the use of the aforementioned layeredtechnique. The temperature coefficient of the thermistor 38 is large andnegative and is used to sense the temperature of the board 10 at alltimes when the board 10 is coupled to its associated electronicanalyzing module as shown in FIGS. 5 and 6. It is operated at relativelylow current levels so the resistance is affected only by the ambienttemperature and not by the applied current.

As before described, external leads 52 and 56 are in metallic electricalconducting contact with a thick film resistor 76 which is provided onthe FIG. 2 side of the substrate layer 12. The resistor 76 is in anhalf-bridge relationship with the thermistor 38 and, as such, itcommonly shares external lead 52 with the thermistor 38; thermistor 38also being in metallic electrical conducting contact with external lead52. The half-bridge circuit configuration is a voltage divider andgenerates a ratiometric output to the module. This is important for itallows the actual resistance values to float and results in highlyconsistent and accurate temperature sensing and control of the board 10on a board to board basis. Accuracy and consistency of the resistor 76and thermistor 38 arrangement is achieved by calibrating the board 10 bylaser trimming of the resistor 76 to produce zero volts at 37° C. Thelaser beam is precisely deflected across the thick film resistor 76 toproduce the desired temperature voltage relationship. A current isapplied at external leads 50 and 52 by the module until zero volts isachieved. This gives a linear output so that the temperatures can bemeasured other than 37° C. from the slope of the line from thecalibration at room temperature and 37° C. The resistor 76 hasessentially zero temperature coefficient and, accordingly, may be placedwithout any adverse effect on the sensing capability of the associatedthermistor 38, on the FIG. 2 side of the board 10 with the heater 74.

Accurate sensing of the ambient temperature of the board 10 is requiredto precisely control the heater 74 to ultimately maintain, within anarrow distribution of temperatures, the desired operating surfacetemperature on the FIG. 1 or sensor side of the board 10.

Placement of the thermistor 38 is another important aspect of thepresent invention. As can be seen in FIG. 1, the thermistor 38 is placedin the same plane and in close relation to the sensors 16, 20 and 24 tothereby accurately sense the ambient temperature at or near suchsensors.

This physical placement of the thermistor 38 allows for the rapidadjustment of the heater 74 by the module to maintain the desiredoperating temperature. The thermistor 38 resistor 76 arrangementprovides temperature measurement accuracy of within ±25° C.

This physical placement of the thermistor 38, so close to the sensors,requires that it be correctly fabricated to ensure that it iselectrically isolated from the electrolytes of the several sensors. Theencapsulant for the thermistor must be thick enough to accomplish theelectrical isolation yet thin enough so as not to lose any responsetime.

The heater 74, provided on the FIG. 2 side of the board 10, rapidly andaccurately produces the necessary heat in response to any temperaturechange sensed by the thermistor 38; the thermistor 38 and the severalsensors 16, 20, and 24 all being in the heated region produced by theheater 74.

Thick film heaters are not generally considered to be rapid responsedevices and their heat output tends to take a relatively long time, interms of electronic devices, to change. To improve the responsiveness ofthe heater 74, it is powered by a controlled DC voltage whereby theheater is regulated by a combination of proportional (P), integral (I)and/or derivative (D) controls, preferably PID control thereby reducingthe amount of overshooting or undershooting by the heater of apredetermined temperature. This not only increases the responsiveness ofthe heater 74 but also allows for better overall thermal controlincluding avoiding the heater 74 from overshooting or undershooting thedesired temperature.

The timing sequence for the production of the heat by the heater 74 tothe several sensors is provided by the natural state of power suppliedto the board 10 when it is connected to the electronic module. This samepower will also produce the read-out from the measurements by thesensors of the blood gas oxygen, carbon dioxide and pH. This timingsequence facilitates a room temperature calibration of the board 10; aelevated temperature calibration at 37° C. and then the measurement ofthe blood gas oxygen, carbon dioxide and pH.

Prior to any measuring of the blood gases by the several sensors 16, 20and 24, all or part of the board 10 may be exposed to or stored with acalibration liquid, with the several sensors being exposed to the fluid.To measure the blood gases, the several sensors are brought in contactwith the volume of the blood sample to be measured. The volume of theblood sample may be quite small, ranging from as small as a fewmicroliters.

FIG. 3 shows the preferred embodiment of the substrate of the presentinvention where two reference electrodes 30A and 30B are present inoffline alignment to the alignment of the sensors 20, 16 and 24 andthermistor 38. The axial alignment shown in FIG. 3 allows the sensors tobe in contact with a sample in a chamber covering their alignment, whilethe reference electrodes can be in contact with reference fluid orelectrolyte in another chamber placed in fluid contact with thereference electrodes. Any alignment pattern can be used that separatesthe reference electrode from the sensors in the aforedescribed manner.The other components of the wiring board are as described for the otherfigures.

FIG. 4 shows a broader aspect of the invention where only one sensor 20is present with one reference electrode 30. If the sensor does notrequire a reference electrode as in the case of most amperometricelectrodes the reference electrode need not be present.

FIG. 5 shows the block diagram of the functions and interrelationship ofthese functions for the electronic analyzing module of FIG. 5,hereinafter referred to as Analyzer with its electrical connection tothe patterned metallic layer 14 of FIGS. 1-4. The analog inputprocessing unit 180 of the Analyzer interfaces with the electriccircuitry patterned metallic layer 14 of the previous figures by theexternal leads 46-60 to allow signals from the sensing electrode 16, 20,and 24 and any temperature detector, thermistor; 38 of FIGS. 1, 3-4.Also the external leads 46-60 allows for electrical current to besupplied to any heater 74 and resistor 76 on board 10 as shown in FIG. 2and for any current or voltage that may be needed by the sensors 18 onthe board 10. The electrical connections to the external leads can beseparate but are preferably individual connections in a bundle connectoror ribbon cable. Connection 181 can carry current to an amperometricoxygen sensor 24 of FIG. 1. Respectively, connections 182, 183, 184, and185 can carry signal and/or supply current or voltage to: the sensors 16and 20, the thermistor 38, and heater 74 all shown in the previous FIG.1 and 20. The processing unit 180 can be electrically connected to themicrocomputer 187 by 186 to the function of a 12 bit analog to digitalconverter 188. Converter 188 can be electrically connected by 189 toline 200 a type of buss line. Through line 200 connections are made tothe central processing unit (CPU) 201 which has is a date/time circuitand battery backup random access memory device and can be and preferablyis an 8-bit central processing unit (CPU) microprocessor. In additionthe encoded information reader and drive circuit unit 190 is connectedby line 191 to the microcomputer 187 through Input/Output (I/O) port 192for two way communication. The CPU is connected through I/O port 195 tothe display and keyboard unit 196, and this unit is connected throughI/O port 197 and through line 202 to line 200 for communication with themicrocomputer 187. The CPU 201 is connected for external communicationby RS232 and drive circuit unit 203 through serial port 204. Themicrocomputer 187 is connected to a power supply 205 and battery pack206 for power. Also input output port 208 is connected electrically to aprinter mechanism 210 for a hard copy display.

In the preferred embodiment, the printed wiring board whose functionsare depicted in FIG. 5 is divided into two boards subassemblies. First aprimary board subassembly which is divided into five subsystems: themicrocomputer, the bar code reader system, the printer subsystem, thesensor input circuits, and the RS232 drive circuit. The secondsubassembly is the power supply board subassembly which is a switchpower supply with four outputs. One pair provides ±5 volts for thedigital and the analog circuits. The other pair provides an isolated ±5volts for the RS232 drive circuits. The microcomputer consists of fourmajor subsections--the central processing unit, the program memory, therandom axis memory, and address decoder and the analog digitalconverter. The CPU is preferably an 80 C51FA8 bit CMOS microcontrollerwith a 256×8 internal random axis memory and four 8 bit bi-directionalparallel ports and three 16-bit timer/event counters and with fullduplex programmable serial interface and reduced power modes. The CPUcan address 64,000 bits of programmed memory and 64,000 bits of randomaccess memory or memory map input/output. The program memory ispreferably a 27C256 which is a high-density CMOS electricallyprogrammable read only memory organized as a 32,768×8 configuration. Therandom access memory is divided into two types. First an 8,000×8volatile static random access memory and a 2,000×8 nonvolatile RAM witha built-in real time clock that uses an embedded lithium energy cell tomaintain the watch information and retain the RAM data for over fiveyears. The address decoder is a GAL that selects seven memory mappedareas of random access memory and two are selected as data memory andthe rest are selected as inputs or outputs. The analog digital converteris an ML2208 data acquisition peripheral that has an eight channelsingle ended multiplexer, a programmable game instrumentation amplifier,a 2.5 volt band gap reference, and a 12-bit+analog to digital converterwith built-in sample-and-hold. The 8D converter interfaces to themicrocontroller through the general purpose 8-bit port. Also, the ML2208includes a programmable processor, data buffering, a 16-bit timer andlimit alarms. The bar code read system consists of a 70 nanometerprecision optical reflective sensor and the system uses the HPHBCS-1100sensor and HP sapphire lens. A printer subassembly is a thermal printersubassembly having four main components--the 8-bit latch, a printer headdrive, a motor drive circuit and the printer mechanism. The sensor inputcircuits are analog signal conditioning circuits that receive thesignals from the sensors and electronically control the sensors. Thereare two types of signals from the sensors, voltage or current. Inaddition, there is the heater control circuit. The serial or port drivercircuit consists of the RS232 input buffer and line driver that areoptically isolated from the internal circuits of the analyzer. Isolationis necessary in order to comply with the UL544 leakage currentrequirement. The power supply circuit supplies the five volts to thelogic circuits and the analog circuit and an isolated five volts for theserial port. Power to the printer motor and printer heads is supplieddirected from the battery pack which is typically six volts.

Any components known to those skilled in the art to accomplish theaforementioned functions can be used in the analyzer and the electricalcircuitry of the present invention.

Although a particular preferred arrangement for the functional units ofthe Analyzer has been specifically set forth variations are possiblethat may delete one or more of the functional units. As long as theprocessing unit 180, and converter unit 188 are present when analogsignals are used, and a processor is functionally tied into these unitsand power is supplied and a read out can be obtained the Analyzer isusable for use with the board 10 in a housing. Appropriate softwareresides in the CPU to accomplish these connections and to convertsignals from the sensors and to perform the calibration and analysis ofsamples and to give values indicating the specific amounts of the knowntypes of analytes present in the analyzed fluids.

FIG. 6 depicts a flow chart for the software of the Analyzer. Thesoftware assists the analyzer in performing several function. One ofthese is in capturing dc voltage levels emitted from the analyte sensorspreferably the oxygen, carbon dioxide, and the pH sensors that are onthe board 10 in a housing. Another is in analyzing a sample byperforming relative measurements on the sensor inputs, while stillanother is to provide an analysis report. In FIG. 6 the unit is turnedon at 120, where the connector 122 indicates that the software duringthe initialization function is responsible for verifying the status ofthe electronic components on the board 10 and of the RS232 communicationport, bar code, detection of the sensor element, non-volatile RAMchecksum, ROM checksum, RAM check as indicated at 124 and the real-timeclock, and valid date and time and display units and printer asindicated at 126. The diagnostic function is responsible for performingthe requested diagnostic function. Diagnostic commands are received atthe RS232 port. The diagnostic commands can be in the form of ASCII datain both upper and lower case alpha characters and the digits 0 thru 9.At the decision block 127, if the analyzer is connected to the sensorthe software enters the calibration mode and the analysis mode andoutputs results. In this operation the emitted sensor voltages areconverted from analog data to 16 bit digital data and the signal levelsare captured, averaged and stored for the calibrant. Signal values fromthese three sensors depict the entry and exit of calibration solution,sample to be analyzed within the sensor channel. Also the levels of theanalytes that exist during the presence of each of the liquids beinganalyzed are depicted. The Units are measured for these variables of theanalytes and displayed in millimeters of mercury when blood gases arethe analytes. In the signal processing phase of the software events areencompassed such as the detection of introduction of the calibrantsolution, setting of any temperature of the calibration solution,introduction of the sample, and analysis of the sample. References tosignal data are interpreted as relative and not absolute. Detecting theentrance, exit and temperature of a sample liquid like blood isperformed by comparing present sensor values processed by the analog todigital converter to previous sensor values. Rise, fall andstabilization of a sensors signal is the means used in detecting achange occurred in the sensor component. The outputs of the analyzer areanalog voltages corresponding to relative levels of the analytes in thesample fluid at the sensor temperature. These voltages are sampled andconverted to a digital value many times per second. Once each secondthese values are averaged to provide a smoothed estimate of theparameter value. The quantitization is bipolar with an good accuracy.Changes in the signal levels are used to detect introduction of thecalibrant and to validate sensor operation. The values measured at theset temperature for the calibrant and sample are used to calculate thetest results. The input units can be millivolts and nano-amperes. Oncethe analyte levels are obtained from the sample like blood gas theanalysis is performed. This is done by the execution of a series ofknown mathematical equations using the analyte data as input. Interceptand slope is entered in the system via the bar code reader. After theanalysis and display of the results electronically and/or by hard copythe software enters the connector and allows for the analyzer to powerdown and turn off.

We claim:
 1. An improved electronic wiring board having a nonconductingsubstrate, temperature sensor and at least one analyte sensor supported,in close relation, one to the other, on the same side of said substrateand a heater, also supported on the substrate, and located on anotherside of said substrate from the temperature sensor and analyte sensor toprovide heat in response to temperature sensed by said temperaturesensor to at least the region where said temperature sensor and saidanalyte sensor are positioned on said substrate to thereby control thetemperature of said region of said board within a narrow distribution oftemperatures, and connecting means supported on said substrate forconnecting said board to an external electrical source.
 2. The improvedelectronic wiring board of claim 1, wherein said board is manufacturedusing thick film layered circuit technique.
 3. The improved electronicwiring board of claim 1, wherein said temperature sensor is a thermistorand said analyte sensor is at least one blood gas sensor, where thetemperature sensor and the analyte sensor are supported in the sameplane on said board.
 4. The improved electronic wiring board of claim 3,wherein said blood gas sensor is at least an oxygen sensor.
 5. Theimproved electronic wiring board of claim 3, wherein said blood gassensor is at least a carbon dioxide sensor.
 6. The improved electronicwiring board of claim 3, wherein said blood gas sensor is at least a pHsensor.
 7. The improved electronic wiring board of claim 3, wherein saidblood gas sensor includes an oxygen sensor, a carbon dioxide sensor anda pH sensor.
 8. The improved electronic wiring board of claim 3, whereinthe substrate of said board is a flat substantially thin ceramicsubstrate layer.
 9. The improved electronic wiring board of claim 8,wherein said board includes a patterned metallic layer provided on saidceramic substrate layer.
 10. The improved electronic wiring board ofclaim 9, wherein said metallic layer is formed on said substrate bydepositing a metallic printing paste on said substrate to formelectronic conducting pathways and the electrodes of said sensors andthe electrode of a reference electrode.
 11. The improved electronicwiring board of claim 10, wherein said metallic layer is encapsulatedwith at least one layer of a chemically stable and moisture resistantencapsulant.
 12. The improved electronic wiring board of claim 8,wherein the thermistor is on the ceramic substrate layer, and saidthermistor is encapsulated with at least one substantially thin layer ofa chemically stable and moisture resistant encapsulant.
 13. The improvedelectronic wiring board of claim 1, which includes a control meanselectrically connected to the board for receiving the output from thetemperature sensor and to power the heater to control the temperature ofsaid region of said substrate within a narrow distribution oftemperatures to adjust the temperature for maintenance of the operatingtemperature.
 14. The improved electronic wiring board of claim 1, whichincludes a means for containing fluid on the board in contact with theat least one analyte sensor.
 15. The improved electronic wiring board ofclaim 1, wherein said heater is powered by pulsed DC whereby said heateris continually turned on and off thereby avoiding said heater fromovershooting or undershooting a predetermined temperature.
 16. Theimproved electronic wiring board of claim 1, wherein said thetemperature sensor senses the ambient temperature of the board and theheater heats the board within the temperature range of ambient to 37°C.±25° C.
 17. An improved electronic wiring board having a nonconductingsubstrate, temperature sensor and at least one analyte sensor supported,in close relation, one to the other, on the substrate and a heater, alsosupported on the substrate, to provide heat in response to temperaturesensed by said temperature sensor to provide heat to at least the regionwhere said temperature sensor and said analyte sensor are positioned onsaid board to thereby control the temperature of said region of saidboard within a narrow distribution of temperatures, connecting meanssupported on said substrate for connecting said board to an externalelectrical source where the connecting means has a plurality of externalleads, a resistor which is supported on said board on the same side assaid heater and commonly connected to one of said external leads withsaid thermistor, dividing the voltage therebetween.
 18. The improvedelectronic wiring board of claim 17, wherein the temperature coefficientof said thermistor is negative or positive and the temperaturecoefficient of said resistor is substantially zero, and where thedivided voltage is proportional or inversely proportional totemperature, the this output is used to measure temperature.
 19. Theimproved electronic wiring board of claim 18, wherein said connectingmeans further includes a plurality electronic conducting pathwaysindividually and electrically connecting each of said sensors and saidthermistor with external leads provided on said board at the end of saidpathways.
 20. The improved electronic wiring board of claim 19, whereinsaid resistor and said heater are each electrically connected toexternal leads.
 21. The improved electronic wiring board of claim 20,wherein said heater is powered by pulsed DC whereby said heater iscontinually turned on and off thereby avoiding said heater fromovershooting or undershooting a predetermined temperature.
 22. Theimproved electronic wiring board of claim 19, wherein said externalleads are positioned on the same side of said board as said resistor andsaid heater.
 23. The improved electronic wiring board of claim 22,wherein said electronic conducting pathways individually andelectrically connecting each of said sensors and said thermistor on oneside of said board with external leads provided on the other side ofsaid board through a plurality of holes in said board.
 24. The improvedelectronic wiring board of claim 19, wherein said thermistor andresistor are calibrated by laser trimming of said resistor.
 25. Theimproved electronic wiring board of claim 24, wherein said oxygen sensoris an electrochemical cell and includes a anode and a cathode, eachconnected to an external lead.
 26. The improved electronic wiring boardof claim 25, wherein said oxygen sensor has an oxygen permeable membranecovering, in a fluid tight manner, a means with an opening in said boardto contain an electrolyte, said anode being grounded on said board tothereby assure that potential of said electrolyte is the same as theanode potential.
 27. The improved electronic wiring board of claim 26,which includes at least one reference electrode, to provide an accuratereference potential, supported on said board and is electricallyconnected to a electronic conducting pathway.
 28. The improvedelectronic wiring board of claim 27, wherein there is one referenceelectrode supported on said board that is electrically connected to aelectronic conducting pathway extending from said anode.
 29. Theimproved electronic wiring board of claim 23, wherein the heateroccupies the opposite side of the board from the thermistor and sensorand has a serpentine circuit layout.
 30. The improved electronic wiringboard of claim 23, wherein at least one analyte sensor is a thick filmelectrode sensor with at least one polymeric membrane and electrolyte.31. An improved temperature control apparatus for an analyte sensor,comprising:a) electronic wiring board having a nonconducting substrate,temperature sensor and at least one analyte sensor supported, in closerelation, one to the other, on the substrate and a heater, alsosupported on the substrate, and located on the substrate to provide heatin response to temperature sensed by said temperature sensor to at leastthe region where said temperature sensor and said analyte sensor arepositioned on said substrate; b) connecting means supported on saidsubstrate for connecting said board to an external control means; and c)control means to receive the output from the temperature sensor andpower the heater to control the temperature of said region of saidsubstrate within a narrow distribution of temperatures.